Mohamed LOUKIL 1,2, Janis VARNA 2 , Zoubir AYADI1 Institut...

PARAMETER DETERMINATION IN DAMAGED LAMINATE MODEL B Y OPTICAL FULL-FIELD MEASUREMENT OF THE DISPLACEMENT USING ES PI

1Institut Jean Lamour, SI2M, Nancy-Université, EEIGM 6 Rue Bastien Lepage, F-54010, Nancy, France2Division of Polymer Engineering, Lulea University o f Technology, SE-97187 Lulea, Sweden

Mohamed LOUKIL1,2 , Janis VARNA2 , Zoubir AYADI1

5th International Conference on Composites Testing and Model IdentificationEPFL, Lausanne, 2011

Where is Luleå?

Luleå

Where is Nancy?

Nancy

Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011 2

Outline

�Introduction : Laminate Damage

�Potential of ESPI for characterizing damaged laminates

�Damage development in a glass fiber/epoxy laminate

Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011

�Damage development in a glass fiber/epoxy laminate

�Conclusion and perspectives

3

Damage in composite

debonding

0° Layer

90° Layer

0° Layer

Initiation (micro-scale)

Propagation (ply-scale)

Transverse cracks

Interface problem:

6/27

Direction

of propagation

0° layer

90° layer

0° layer

Delamination

Transverse

crack

Transverse crack continues to propagate

Delamination

Interface problem:

Fiber/matrix

Transverse crack Delamination


-70°70°

70°

0°

0°

σσσσxσσσσx

X

Z

y

Crack surface

Crack surface

y

σσσσxσσσσx

x→Laminate length (Tensile axis)y→Laminate widthz→Laminate thickness

COD : Crack Opening DisplacementCSD : Crack Sliding Displacement

CSD

x

y

z.


Why we want to measure COD and CSD?

2

2112

012

0290

0

1

121

1

−−

+

=

νννν xy

x

x

x

E

E

h

tCOD

E

E

“Glob-Loc” approach (Janis VARNA)

COD(opening) and CSD(sliding) govern

the stiffness reduction

�These parameters are calculated for 90° layer using linear

Which technique we are going to use?


�These parameters are calculated for 90° layer using linear elastic models: Shear lag, Hashins and FEM

�To prove that these results are correct

Basic Principles of ESPIFull Field Method: Interferometry of SpeckleESPI (Electronic Speckle Pattern Interferometry)

LaserWavelength = 0.6328 µmPower = 30 mW

The area of study is lit by two beams coming for the same laser

9/27Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011 7

Before displacement

Speckle before displacement


x

y

8

After displacement


x

y

9

Speckle after displacement Speckle before displacement

-Subtraction

=

Results Filtering Demodulating

=

1 542 3Steps:

Speckle after

displacement

Speckle before

displacement

Fringes

map

Filtered fringes

map

Displacement

map


Displacement map

Measurement field: about 1 cm

x

z


x

y

Z

.

about 1 cm

Advantages of ESPI� Full field imaging of displacement with a resolution of 10 nanometers.

�Measurements can be done on a variety of materials and the displacements undermechanical and thermal loads can be measured along three perpendicular axis withoutcontact with the sample.

�ESPI offers the unique possibility to measure both, the in-plane and out-of-planedisplacement without surface preparation.

Drawbacks of ESPIDrawbacks of ESPI� Complexity, high costs of optical setups, difficulties in aligning of the opticalelements.

�There are problems in working outside the laboratory especially due to high sensitivity ofESPI devices against environmental vibrations and daylight.

� Range of the measurable displacement: about a few micrometers


E1= 44.7 GPa

E2

= E3

= 12.7 GPa

G12

= G13

= 5.8 GPa

G23

= 4.885 GPa

ν12

= ν13

= 0.297

ν23

= 0.3

The [0,704,-708,704,0] laminate was made ofglass fiber/epoxy.Specimen of 19.5 mm width, the thickness is2.75 mm and reinforced with GF/EP end tabs inthe gripping area.

Materials1.3751.222

0.611

0

-0.611

0°

+70°

+70°

-70°

Z (mm)

X

Damage evolution by increasing the stress σσσσ

13/27

-1.222-1.375

+70°

0°


Crack surface

Crack surface

y

σσσσxσσσσx

In plane displacement measurement

CSD

RDx

yz.

Measurement directionθθ cossin ×+×= CSDCODRD x


Symmetric illuminations: themeasurement is along a direction(x) of the studied surface

Bisector

14

Relative Displacement in (-70 °) layer

0.18

9 µm

196

µm

RD1n=0.380 µm/MPa

Crack 1 Crack 2R

elat

ive

Dis

plac

emen

t(µ

m)

0.18

9 µm

196

µm


0.19

6 RD1n=0.380 µm/MPa

RD2n=0.394 µm/MPa

15

xz

Rel

ativ

e D

ispl

acem

ent

Pixels

Profile of the X-direction relative displacement along the mid-plane (on the specimen edge) corresponding to a variation of the relative average stress (∆σ = 0.497MPa).

0.19

6

Relative Displacement in (70 °) layersR

elat

ive

Dis

plac

emen

t(µ

m)

Relative displacement profile along the X-axis in the midplane of the 70°ply. ( ∆σ = 0.497 MPa)


0°70°

70°0°

-70°

Rel

ativ

e D

ispl

acem

ent

Pixels

16

xz

Relative Displacement in (0°) layersR

elat

ive

Dis

plac

emen

t(µ

m)

Relative displacement profile along the X-axis in the midplane of the 0°ply. ( ∆σ = 0.497 MPa)


0°70°

70°0°

-70°

Rel

ativ

e D

ispl

acem

ent

Pixels

17

xz

Out of plane displacement measurement

CSD

Crack surface

Crack surface

RD

y

z.

σσσσxσσσσx


Non Symmetric illuminations:the measurement is perpendicular to the fiber direction

RDx.

Measurement direction

Bisector

We are measuring COD directly

18

Crack 1 Crack 2

CODn1= 0.300 µm/MPa

166

µm

0.16

0 µm

Rel

ativ

e D

ispl

acem

ent

(µm

)

COD measurement


Profile of the X-direction COD along the mid-plane (on the specimen edge) corresponding to a variation of the relative average stress (∆σ = 0.533MPa).

CODn2=0.311 µm/MPa0.16

6

Rel

ativ

e D

ispl

acem

ent

Pixels

19

xz

RDn CODn CSDn COD/CSD

Crack 1 0.380 0.300 0.286 1.049

Crack 2 0.394 0.311 0.297 1.047

Comparison of COD and CSDFor (-70°) layer


θθ cossin ×+×= CSDCODRD

θθ

cos

sinCODDRCSD

−=

20

Interactive cracks

RD1n = 0.200 µm/MPa



RD = 0.257 µm/MPa

Crack 1

Crack 2

Crack 3

Crack 4

Rel

ativ

e D

ispl

acem

ent

(µm

)



Profile of the X-direction COD along the mid-plane (on the specimen edge) corresponding to a variation of the relative average stress (∆σ = 0.569MPa).

Rel

ativ

e D

ispl

acem

ent

Pixels

21

0,010

0,015

0,020

CO

D (

mm

)

[0 , +704 , -704]S

Crack Opening Displacement in (-70°) layer by FEM[0, 704, -704]s

0.25 Experimental points

Elliptical model (fitted)

0,000

0,005

0,010

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

CO

D (

mm

)

Z Coordinate (mm)

Actual Crack Profile

Elliptical Profile

Actual Crack Profile = Elliptical Profile

Good relation with the results found by Farge et al . [1]

[1] Farge. L, Ayadi. Z, Varna. J. Optically measured full-field displacements on the edge of a cracked composite laminate. Science direct composites 2008; Part A 39, 1245-1252

17/27Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011 22

0

0.05

0.1

0.15

0.2

0 5 10 15 20 25z (pixels)

CO

D (

µm

)

Elliptical model(interpolated)

2)(1)0()(a

zCODzCOD −=

Elliptical model

Conclusion

ESPI Potential for characterizing damage in laminat es

�Displacement field on the edge of a cracked laminate

�Typical profile the displacement for each ply

�Displacement jumps (cracks) can be measured,


�By changing the directions of laser beams, the COD is directlymeasured; the comparison between COD and CSD is done in thiswork.

�The ratio COD/CSD depends on the material and on the plyorientation.

23

Perspectives

� Comparison with micromechanics models.

� Investigate the effect of interaction between cracks

� Delamination effect on COD

� Cracking in fatigue


Thank you for your attention!your attention!


Camera

θθθθ

θθθθ

2

Δxδ2

M’

M∆x

λ

)(πδ

λ

πδ

λ

π θφ sin42221 =+=∆

θθθθ

1

1’

M’

Mohamed LOUKIL 1,2, Janis VARNA 2 , Zoubir AYADI1 Institut...

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